Porcine reproductive and respiratory syndrome (PRRS) is an acute, febrile, and highly contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). Glycoprotein 5 (GP5) is a glycosylated envelope protein encoded by the PRRSV ORF5, which has good immunogenicity and can induce the body to produce neutralizing antibodies. Therefore, study of GP5 protein is of great significance in the diagnosis, prevention, and control of PRRSV and the development of new vaccines. We reviewed GP5 protein genetic variation, immune function, interaction with viral protein and host proteins, induction of cell apoptosis, and stimulation of neutralizing antibodies. GP5 protein’s influence on virus replication and virulence, as well as its use as a target for viral detection and immunization are reviewed.

Background: Alongshan virus (ALSV) is a novel discovered segmented flavivirus associated with human febrile illness in northeastern China. Ixodes persulcatus is considered as a candidate vector of ALSV in the endemic regions. However, the role of domesticated animals in the circulation and transmission of ALSV have not been investigated. To evaluate the prevalence of ALSV infections in domesticated animals, viral RNA and viral specific antibodies were detected in sheep and cattle in Hulunbuir of northeastern Inner Mongolia. The findings contribute to the understanding of the ecology and transmission of ALSV among different natural hosts. Methods: A total of 480 animal serum samples were collected in Hulunbuir of northeastern China in May, 2017. Viral specific antibodies were tested by indirect enzyme-linked immunosorbent assay (ELISA) with a purified E. coli recombinant capsid protein (VP2) of ALSV (strain H3) and further detected by viral neutralization test (VNT). RNA in serum samples were extracted and detected for ALSV sequence by quantitative real-time RT-PCR. ALSV RNA positive samples were used for virus isolation. Results: ALSV-specific antibodies were detected in 9.2% (22/240) of examined sheep and 4.6% (11/240) of examined cattle by ELISA, while lower serological positivity with 4.2% (10/240) for sheep and 1.7% (4/240) for cattle was confirmed by VNT. In contrast, the prevalence of ALSV RNA was much higher, ranging from 26.3% (63/240) in sheep to 27.5% (66/240) in cattle. The partial S1 (NS5-like) and S3 (NS3-like) segments of ALSVs in sheep and cattle shared high identities of more than 98% to the human and tick isolates in the studied regions. Conclusions: These results suggest that the natural infection of ALSV can be found in sheep and cattle in the endemic regions.

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), which has been regarded as a persistent challenge for the pig industry in many countries. PRRSV is internalized into host cells by the interaction between PRRSV proteins and cellular receptors. When the virus invades the cells, the host antiviral immune system is quickly activated to suppress the replication of the viruses. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate the host machine and circumvent against the host antiviral responses. Therefore, identification of virus–host interactions is critical for understanding the host defense against viral infections and the pathogenesis of the viral infectious diseases. Most viruses, including PRRSV, interact with host proteins during infection. On the one hand, such interaction promotes the virus from escaping the host immune system to complete its replication. On the other hand, the interactions regulate the host cell immune response to inhibit viral infections. As common antiviral drugs become increasingly inefficient under the pressure of viral selectivity, therapeutic agents targeting the intrinsic immune factors of the host protein are more promising because the host protein has a lower probability of mutation under drug-mediated selective pressure. This review elaborates on the virus–host interactions during PRRSV infection to summarize the pathogenic mechanisms of PRRSV, and we hope this can provide insights for designing effective vaccines or drugs to prevent and control the spread of PRRS.

Porcine reproductive and respiratory syndrome (PRRS) is a contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRS is also called “blue ear disease” because of the characteristic blue ear in infected sows and piglets. Its main clinical features are reproductive disorders of sows, breathing difficulties in piglets, and fattening in pigs, which cause considerable losses to the swine industry. NSP9, a non-structural protein of PRRSV, plays a vital role in PRRSV replication and virulence because of its RNA-dependent RNA polymerase (RdRp) structure. The NSP9 sequence is highly conserved and contains T cell epitopes, which are beneficial for the development of future vaccines. NSP9 acts as the protein interaction hub between virus and host during PRRSV infection, especially in RNA replication and transcription. Herein, we comprehensively review the application of NSP9 in terms of genetic evolution analysis, interaction with host proteins that affect virus replication, interaction with other viral proteins, pathogenicity, regulation of cellular immune response, antiviral drugs, vaccines, and detection methods. This review can therefore provide innovative ideas and strategies for PRRSV prevention and control.

Porcine circovirus disease poses a significant threat to the pig farming industry. Globally, four genotypes of porcine circovirus are circulating, with porcine circovirus type 2 and 3 (PCV2 and PCV3) being most strongly associated with clinical manifestations. The recently discovered porcine circovirus type 4 (PCV4) exhibits clinical symptoms resembling porcine dermatitis nephropathy syndrome. This study aimed to assess the prevalence and genetic characteristics of PCVs in Guangdong province, China. A comprehensive analysis was conducted on 193 samples collected from 83 distinct pig farms during the period of 2017–2023. A conventional PCR was employed to investigate the presence of PCV2, PCV3, and PCV4. Among the samples, 56.48%, 8.81%, and 8.81% tested positive for PCV2, PCV3, and PCV2/3 co-infection, respectively. Interestingly, PCV4 was not detected. Whole-genome sequencing was performed on 80 PCV2 isolates and 7 PCV3 isolates. A phylo-genetic analysis revealed that 12 strains belonged to PCV2a, 8 strains belonged to PCV2b, and 60 strains belonged to PCV2d, indicating the prevailing presence of PCV2d in Guangdong province, China. Furthermore, two PCV3 isolates were classified as PCV3a and five strains as PCV3b. Notably, an in-depth analysis of the Cap protein sequence of the PCV2 and PCV3 isolates identified high-frequency mutation sites located in predicted epitope regions. Overall, this study provides valuable insights into the prevalence and evolution of PCV2 and PCV3 during the period of 2017–2023 in Guangdong province, China, thereby contributing to the development of effective prevention and control measures.